1. The Field of the Invention
The present invention relates to spin-valve sensors for reading information signals from a magnetic medium and more particularly to novel structures for spin-valve sensors and magnetic recording systems which incorporate such sensors.
2. The Relevant Art
Computer systems generally utilize auxiliary memory storage devices having magnetic media on which data can be written and from which data can be read for later use. A direct access storage device, such as a disk drive incorporating rotating magnetic disks, is commonly used for storing data in magnetic form on the disk surfaces. Data are recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic recording heads carrying read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, a giant magnetoresistance (GMR) head carrying a spin-valve sensor is now extensively used to read data from the tracks on the disk surfaces. This spin-valve sensor typically comprises two ferromagnetic films separated by an electrically conducting nonmagnetic film. The resistance of this spin-valve sensor varies as a function of the spin-dependent transmission of conduction electrons between the two ferromagnetic films and the accompanying spin-dependent scattering which takes place at interfaces of the ferromagnetic and nonmagnetic films.
In the spin-valve sensor, one of the ferromagnetic films, referred to as a pinned layer, typically has its magnetization pinned by exchange coupling with an antiferromagnetic film, referred to as a pinning layer.
The magnetization of the other ferromagnetic film, referred to as a xe2x80x9csensingxe2x80x9d or xe2x80x9cfreexe2x80x9d layer is not fixed, however, and is free to rotate in response to the field from the magnetic medium (the signal field). In the spin-valve sensor, the GMR effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the sensing layer. Recorded data can be read from a magnetic medium because the external magnetic field from the magnetic medium causes a change in the direction of magnetization in the sensing layer, which in turn causes a change in the resistance of the spin-valve sensor and a corresponding change in the sensed voltage.
FIG. 1 shows a typical prior art GMR head 100 comprising a pair of end regions 103 and 105 separated by a central region 102. The central region 102 is formed by depositing a spin-valve sensor 128 onto a bottom gap layer 118, which is previously deposited on a bottom shield layer 120, which is, in turn, previously deposited on a substrate. Two end regions 103 and 105 abut the edges of the central region 102. In the spin-valve sensor 128, a ferromagnetic sensing layer 106 is separated from a ferromagnetic pinned layer 108 by an electrically conducting nonmagnetic spacer layer 110. The magnetization of the pinned layer 108 is fixed through exchange coupling with an antiferromagnetic pinning layer 114. This spin-valve sensor includes seed layers 116, on which the pinning, pinned, spacer and sensing layers of the spin-valve sensor 128 grow with preferred crystalline textures during sputtering so that desired improved GMR properties are attained. The end regions 103 and 105 are also formed by depositing longitudinal bias (LB) and conducting lead layers 126 on the bottom gap layer 118 and at the spin-valve sensor 128. The end regions 103, 105 abut the central region 102. The central and end regions are sandwiched between electrically insulating nonmagnetic films, one referred as a bottom gap layer 118 and the other referred as a top gap layer 124.
The disk drive industry has been engaged in an ongoing effort to increase the recording density of the hard disk drive, and correspondingly to increase the overall signal sensitivity to permit the GMR head of the hard disk drive to read smaller changes in magnetic fluxes. The major property relevant to the signal sensitivity of a spin-valve sensor in the GMR head is its GMR coefficient. A higher GMR coefficient leads to higher signal sensitivity and enables the storage of more bits of information on a disk surface of a given size. The GMR coefficient of the spin-valve sensor is expressed as xcex94RG/RH, where RH is a resistance measured when the magnetizations of the free and pinned layers are parallel to each other, and xcex94RG is the maximum giant magnetoresistance (GMR) measured when the magnetizations of the free and pinned layers are antiparallel to each other.
In certain spin-valve sensors, particularly those with Coxe2x80x94Fe/Nixe2x80x94Fe films as sensing layers 106, a cap layer 112 is often formed over the sensing layers. The cap layer 112 serves several purposes, and plays a crucial role in attaining a high GMR coefficient. For instance, a Cu cap layers is thought to induce spin filtering, while a Cuxe2x80x94O cap layer is thought to induce specular scattering. Both spin filtering and specular scattering are believed to increase the GMR coefficient of a spin-valve sensor. In addition, a cap layer may be employed to prevent the underlying sensing layers from interface mixing occurring immediately during depositions and oxygen diffusion occurring during subsequent annealing, thereby maintaining suitably soft magnetic properties of the sensing layer and improving the thermal stability of the spin-valve sensor. The term xe2x80x9csoft magnetic propertyxe2x80x9d refers to the capability of a spin-valve sensor to sense very small magnetic fields.
Currently, a Ta cap layer is used in many conventional spin-valve sensors. However, the Ta cap layer does not exhibit desired specular scattering, and is considered inadequate in preventing the sensing layers from interface mixing and oxygen diffusion. Interface mixing originates from direct contact between the sensing layers and the Ta cap layer, and causes a substantial loss in the magnetic moment of the sensing layers. For one currently used spin-valve sensor with 0.32 memu/cm2 sensing layers, this magnetic moment loss accounts for 25% of the magnetic moment of the sensing layers. Oxygen diffusion originates from low passivity of the Ta cap layer, which oxidizes continuously and entirely during annealing, such that oxygen eventually penetrates into the sensing layers, causing more losses in the magnetic moment of the sensing layers.
Another limiting factor of the disk drive recording density is the dimensions of the GMR head. The recording density of the disk drive is inversely proportional to the total thickness of the spin-valve sensor, the gap layers 118 and 124. In other words, in order to increase the disk drive recording density the thicknesses of the spin-valve sensor, the gap layers 118 and 124 must be decreased. Several challenges have arisen in the miniaturization of the gap layers 118 and 124.
The primary duties of the gap layers 118 and 124 are to prevent electrical shorting between the spin-valve sensor 128 and the shield layers 120 and 130, and thus to ensure the functionality of the spin-valve sensor 128. In order to prevent this electrical shorting, a spin-valve sensor must be sandwiched between gap layers 118 and 124 of substantial thicknesses. The gap layers 118 and 124 have been a limiting factor in the miniaturization of the GMR head 100, because as the thicknesses of the gap layers 118 and 124 decreases, the possibility of electrical shorting increases, causing the GMR head to be non-functional.
Thus, it can be seen from the above discussion that there is a need existing in the art for an improved spin-valve sensor with an increased GMR coefficient, and for improved gap layers with decreased thicknesses.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available GMR heads. Accordingly, it is an overall object of the present invention to provide an improved GMR head that overcomes many or all of the above-discussed shortcomings in the art.
To achieve the foregoing object, and in accordance with the invention as embodied and broadly described herein in the preferred embodiments, an improved GMR head comprises an improved spin-valve sensor and improved top and bottom gap layers formed using a deposition/in-situ oxidation process of the present invention. A method of the present invention is also presented for forming a gap layer from a plurality of in-situ oxidized metallic films using the deposition/in-situ oxidation process.
In one embodiment, the top and bottom gap layers preferably formed of multilayer in-situ oxidized Al films are formed on a wafer. The deposition/in-situ oxidation process is repeated until selected thicknesses of the top and bottom gap layers are attained. Full in-situ oxidization of the top and bottom gap layers is preferred for attaining high breakdown voltages.
The improved GMR head of the present invention is preferably incorporated within a disk drive system configured substantially in the manner described above. In addition, the spin-valve sensor of the improved GMR head of the present invention may comprise a cap layer formed of an in-situ oxidized metal film. In one embodiment, the film is Al, Hf, Si, Y, or Zr. In alternate embodiments of the invention, a noble metallic film, e.g., Au, Cu, Rh, or Ru may be sandwiched between a sensing layer and an in-situ oxidized cap layer.
In one embodiment, a bottom shield layer preferably formed of a Nixe2x80x94Fe film and a bottom gap layer preferably formed of an Al2O3 film are deposited on a wafer. Multiple seed layers preferably formed of Al2O3, Nixe2x80x94Crxe2x80x94Fe and Nixe2x80x94Fe films are deposited on the bottom gap layer. A pinning layer preferably formed of a Ptxe2x80x94Mn film is then deposited on the multiple seed layers. Pinned layers preferably formed of Coxe2x80x94Fe, Ru and Coxe2x80x94Fe films are then deposited on the pinning layer. A spacer layer preferably formed of an oxygen-doped, in-situ oxidized Cuxe2x80x94O film is then deposited on the pinned layer. Sensing layers preferably formed of Coxe2x80x94Fe and Nixe2x80x94Fe films are then deposited on the spacer layer. A cap layer preferably formed of an in-situ oxidized Al film (Alxe2x80x94O) is then formed on the sensing layer with a deposition/in-situ oxidization process. In-situ oxidization is preferred for attaining a high GMR coefficient.
The deposition/in-situ oxidation process preferably comprises depositing a metallic film in a vacuum in a DC magnetron sputtering module, and then conducting the in-situ oxidization for a wide range of time in a wide range of oxygen pressures in an oxidation module. In one embodiment given by way of example, the in-situ oxidization is conducted for a period of about 8 minutes in an oxygen gas of about 0.5 Torr. In another embodiment given by way of example, the in-situ oxidization is conducted for a period of about 4 minutes in an oxygen gas of about 2 Torr. The exposure to oxygen is preferably conducted with a moderate temperature, such as ambient room temperature.
The top and bottom gap layers are preferably deposited using the deposition/in-situ oxidization process of the present invention. In order to achieve designed thicknesses, multiple layers may be alternatively deposited and in-situ oxidized using the deposition/in-situ oxidation process. Preferably, when forming the top and bottom gap layers, the alternating oxidized layers are fully oxidized.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.